This invention relates to handwriting recognition and, more particularly, to handwriting recognition for hand-held pen computers and the like.
The basic Unistrokes application describes a handwriting recognition system and methodology which utilizes continuous, explicitly delimited strokes for representing natural language symbols at the atomic level (i.e., alphanumeric characters for English and other orthographic natural language representations, and phonemes for phonetic systems). Additional strokes of like type can be interspersed with these symbol representing strokes for control purposes, such as for switching between look-up tables for lower and upper case characters and for less frequently utilizes punctuation marks, text editing functions and special constructs (e.g., equations). See, for example, a copending, commonly assigned U.S. patent application of Dennis Venable, which was filed Jan. 3, 1995 under Ser. No. 08/368,122 on xe2x80x9cSELF-DELIMITING SPECIFICATION OF MULTIDIMENSIONAL CHARACTER CONSTRUCTIONS FOR PEN COMPUTERS.xe2x80x9d (now abandoned) Furthermore, the usual single stroke per natural language symbol characteristic of the Unistroke alphabet may be relaxed if desired to permit some or all of the natural language symbols to be represented by multiple, separately delimited strokes, such as may be needed or desired for applications involving larger natural language symbol sets. See, for example, a copending, commonly assigned U.S. patent application of Robert R. Buckley, which was filed Jan. 3, 1995 under Ser. No. 08/368,136 on xe2x80x9cEXTENDED SELF-DELIMITING DATA ENTRY FOR PEN COMPUTERS,xe2x80x9d (now abandoned).
Successive Unistroke symbols are positively delimited from each other by a predetermined, intervening, stroke independent delimiting operation, such as the waiting for writing these symbols into a pen computer or the like. This positive delimiting of successive Unistroke strokes significantly simplifies the recognition process by parsing the respective strokes completely independently of their spatial relationship while capturing the logical ordering of these strokes based on the time order in which they are written. Thus, the Unistroke symbollogy and recognition process are well suited for applications in which spatial ordering of stroke-by-stroke cyclical changes in the pressure atypical user causes a stylus or electric pen to exert against a writing surface during and following, respectively, while symbols is difficult to achieve or assure, such as xe2x80x9cheads-upxe2x80x9d writing and/or for applications requiring the writing of symbols on small writing surfaces that are too small to maintain an easily recognizable spatial separation between logically ordered symbols that are written on a scale that is natural and comfortable to the ordinary user.
The basic Unistrokes application recognizes that the symbol recognition process is further simplified if the Unistroke symbols are well separated from each other in xe2x80x9csloppiness space.xe2x80x9d As set forth in the basic Unistrokes application, this xe2x80x9csloppiness spacexe2x80x9d notion can best be understood by recognizing that each alphanumeric symbol is defined by some number of features (say, d features). Thus, each symbol nominally resides at a unique point in a d-dimensional space which is referred to herein as xe2x80x9csloppiness space.xe2x80x9d From this it follows that the amount of overlap, if any, that occurs in the positioning within this d-dimensional space of the normal variants of the symbols of a given alphabet determines how well separated those symbols are in sloppiness space. If there is little, if any, overlap between the variants of different symbols, the symbols are xe2x80x9cwell separated from each other in sloppiness space.xe2x80x9d This goal is well met by the Unistroke alphabet that is disclosed in the basic Unistrokes application when the symbols are written by different users under reasonably consistent conditions. In practice, however, it has been found that the tilt angle at which different users tend to write strokes on easily rotatable writing surfaces, such as the input interfaces of hand-held computers, is a user dependent variable which varies significantly from user-to-user. Some users intuitively compensate for rotational tilt of the writing surface by generally referencing their strokes to the principal axis of the writing surface, but other users tend to reference their strokes to other features of their environment, such as the principal axis of their bodies. Thus, the rotational tilt of the writing surface sometimes introduces an unwanted ambiguity that reduces the reliability of the character recognition process. Accordingly, it would be desirable to avoid this ambiguity, especially if that can be done without interfering with the users"" normal work practices.
To that end, the present invention defines a Unistrokes symbollogy in which strokes of like profile (i.e., strokes that are distinguished from each other by their rotational orientation) are rotationally offset from each other by at least 90xc2x0. This provides a sufficient tolerance for disambiguating these strokes when they are written into hand-held pen computers and the like by users having widely divergent hand writing styles.